1. Field of the Invention
The present invention relates to a recording medium having a read-only storage area and a writable storage area and a recording/reproducing apparatus and method therefor, and more particularly, to a recording medium having a read-only storage area complying with a digital versatile disc (DVD) specification and a writable storage area physically compatible with a DVD-writable specification and a recording/reproducing apparatus therefor.
2. Description of the Related Art
Generally, read-only optical recording media that are manufactured by injection molding have characteristics in that information is configured in the form of embossments referred to as pits so that user information is recorded on a mold, and the information is transferred during injection. Accordingly, read-only optical recording media are advantageous in increasing production efficiency compared to the case where information is recorded on a floppy disc or a magnetic recording medium and distributed.
However, read-only optical recording media on which users cannot record data have a problem in that data cannot be modified or added in application examples such as an encyclopedia and popular music data for accompaniment which frequently require modification of data and addition of data.
Meanwhile, among digital versatile disc specifications, read-only discs are defined in a digital versatile disc read only memory (DVD-ROM) specification (DVD Specification for read-only memory Part 1 version 1.0). Discs on which a user can record data are defined in a digital versatile disc random access memory (DVD-RAM) specification (DVD Specification for rewritable memory Part 1), in a digital versatile disc recordable memory (DVD-R) specification (DVD Specification for recordable memory Part 1), and in a digital versatile disc rewritable memory (DVD-RW) specification (DVD Specification for re-recordable memory Part 1).
However, discs having both a read-only specification and a recordable specification are not defined so that requirements for modification of data and addition of data, which are characteristics of a recordable disc, and requirements for mass copying of the same data, which is a characteristic of a read-only disc, cannot be simultaneously satisfied.
When proposing a new optical disc satisfying the above requirements, compatibility with a recording/reproducing apparatus according to a conventional specification should be considered. In other words, it is important to make a new optical disc satisfying the above requirements to be compatible with a conventional recording/reproducing apparatus which is made and performs, without consideration of a medium having the characteristics of both a recordable disc and a read-only disc.
In this case, it is apparent that complete compatibility cannot be achieved because the characteristic of a particular area on a single disc changes. Accordingly, as for compatibility, the characteristics of a read-only medium are primarily considered such that data in a read-only storage area can be reproduced in a conventional apparatus for only reproducing, and simultaneously, a writable storage area is considered to be compatible with physical recording/reproducing characteristics defined in a conventional rewritable specification taking into account the fact that data can be additionally recorded or updated in the writable storage area while a user is using a disc.
In addition, it is preferable that an optical recording medium having a read-only storage area and a writable storage area has drive compatibility with a conventional DVD-ROM drive and a conventional DVD-RAM drive.
For a clear understanding of the present invention, a structure of an optical disc (optical recording medium) defined according to a digital versatile disc read only memory (DVD-ROM) specification will be described in detail. FIG. 1 is a sectional view of a conventional dual layer optical disc 10 defined according to the DVD-ROM specification. The optical disc 10 defined according to the DVD-ROM specification comprises first and second substrates 12, 14. Information layers 16, 18 are formed on the first and second substrates 12, 14, respectively, and the first and second substrates 12, 14 are united such that the information layers 16, 18 face each other. The information layer (16 in this instance) nearer to a substrate on which a read laser beam is incident is defined as a first recording layer, and the underlying information layer (18 in this instance) is defined as a second recording layer.
Such an optical disc 10 includes a lead-in area (not show) at an innermost part of the optical disc 10 and a lead-out area (not shown) at an outermost part of the optical disc 10, or a middle area in which various control information (not shown) and information on the physical characteristics of the optical disc 10 is recorded, so that data in the inner part and the outer part can be steadily read.
Generally, a read-only optical disc is molded by injecting a polycarbonate resin material into a die, referred to as a stamper, on which information is formed in the form of embossed pits, such that the information can be transferred to the read-only disc. After forming the read-only optical disc by injection, a material such as aluminum having a characteristic of reflecting light is sputtered on an information surface to form a reflective layer.
A DVD-ROM (the optical disc 10) is formed by uniting two discs (the first and second substrates 12, 14), each of which is molded according to the above method to have a thickness of 0.6 mm, so as to have a total DVD-ROM thickness of 1.2 mm. One substrate may not have a recording layer, or each substrate may have two recording layers. In the case where each of first and second substrates 12, 14 has a single recording layer, when the optical disc is formed such that data can be read from only one side of the optical disc, the optical disc is referred to as a dual layer optical disc. When a disc is formed such that data can be read from layers on both sides of the optical disc 10, the optical disc 10 is referred to as a double sided disc.
As described above, since information is recorded on a read-only optical disc while it is being formed by injecting a polycarbonate resin material into a stamper on which information is formed, the information can be formed on the read-only optical disc in a short time as compared to a magnetic recording medium or a writable recording medium. Accordingly, the read-only optical disc is suitable for mass producing the same data, such as a film or a computer game which needs to be copied in large quantity.
FIG. 2 is a diagram showing a structure of a conventional optical disc recording medium 20 having two data storage areas having different characteristics. Data which can be reproduced using a laser of 780 nm is recorded in a first recording area 26 on the optical disc 20, and data which can be reproduced using a laser of 635-650 nm is recorded in a second recording area 27. Referenced numeral 22 denotes a standard density information layer for a compact disc (CD), reference numeral 23 denotes a high-density information layer for a DVD, reference numeral 24 denotes a second substrate layer, reference numeral 25 denotes a first substrate layer, reference numeral 26 denotes the first recording area which is readable using the laser of 780 nm, and reference numeral 27 denotes the second recording area which is readable using the laser of 635-650 nm. The dual layer high-density optical disc 20 of FIG. 2 is disclosed in U.S. Pat. No. 5,732,065, entitled “Optical Information Carrier Including Standard and High Density Layers,” and filed on Sep. 4, 1996.
FIG. 3 shows a structure of a complex recording layer 32 of a typical writable, optical recording medium 30. Since user data is not recorded on a disc during manufacturing of a writable medium such as a digital versatile disc random access memory (DVD-RAM), substrates can be formed using the same stampers. Unlike a read-only medium in which a reflective layer is simply formed, a complex recording layer including a plurality of films (i.e., a dielectric layer 34, a recording layer 36, another dielectric layer 38 and a reflective layer 40 shown in FIG. 3) needs to be formed on a substrate 42 to allow a user to record data on the optical recording medium 30. A DVD-RAM or a digital versatile disc-rewritable (DVD-RW) has a complex recording layer having a multi-layered structure such that recording can be achieved using a change in a material of the recording layer 36, that is, a change between an amorphous state and a crystalline state